Could We Explore the Entire Galaxy With Self-Replicating Robots?

Scientists and engineers since the 1940s have been toying with the idea of building self-replicating machines, or von Neumann machines, named for John von Neumann. With recent advances in 3D printing (including in zero gravity) and machine learning AI, it seems like self-replicating machines are much more feasible today. In the 21st century, a tantalizing possibility for this technology has emerged: sending a space probe out to a different star system, having it mine resources to make a copy of itself, and then launching that one to yet another star system, and on and on and on.

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As a wild new episode of PBS's YouTube series Space Time suggests, if we could send a von Neumann probe to another star system—likely Alpha Centauri, the closest to us at about 4.4 light years away—then that autonomous spaceship could land on a rocky planet, asteroid, or moon and start building a factory. (Of course, it'd probably need a nuclear fusion drive, something we still need to develop.)

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That factory of autonomous machines could then construct solar panels, strip mine the world for resources, extract fuels from planetary atmospheres, build smaller probes to explore the system, and eventually build a copy of the entire von Neumann spacecraft to send off to a new star system and repeat the process. It has even been suggested that such self-replicating machines could build a Dyson sphere to harness energy from a star or terraform a planet for the eventual arrival of humans.

This process would hypothetically take millions of years to cross the entire galaxy, assuming our self-replicating, factory-building spaceships can travel at about 10 percent the speed of light and that they take about 500 years to extract the necessary resources to build a complete copy of themselves. But because each probe could make multiple copies of itself, the entire galaxy would be covered with von Neumann probes by the end of those millions of years.

This brings up another question: If we are nearing the technological sophistication to pull this off, why don't we see the remnants of self-replicating machines strewn across the galaxy from other intelligent life? This, of course, is part of the larger Fermi paradox that asks why we have no evidence of alien intelligence ever existing, despite that fact that many statistical models like the Drake equation suggest that intelligent life should be all over the place. Maybe civilizations destroy themselves before they can achieve such technological triumphs. Maybe intelligent life turns to a virtual world and abandons the effort to explore the physical one. Maybe the probability of organic chemicals finding the right conditions to become life is really that astronomically small, or the probability that life makes the jump from microbes to intelligent life is that small.

And another philosophical question: If these robots reproduce on their own, and can continue hopping from star system to star system while humans stay stuck on Earth, who has really colonized the galaxy?